why not just use light 38sp bullets and loads in the long cases rather than messing with a bunch of different case sizes.

The Cadet cannot always be made to feed the Maximum, it's to long to turn the corner.  The rim binds in the feed tray and the bullet binds in the chamber. This is not true in all Cadets, some will feed some will not.

There are those who modify the feed tray  to allow the cartridge to feed. The feed tray can be widened in the Cadet but should never be deepened.  Deepening can weaken the breech block.  The Breech block is also your "locking lug".

You can also adjust the notch between the horns of the lever so the block drops a little further, but this only gives marginal additional clearance.

Best thing to do is make a dummy cartridge and see if it will feed in the chamber without modification.  If it fits, all well and good.  If it doesn't look for a different action.  

The other problem I have seen noted with one .357 Maximum  Cadet was bulged chamber. The tenon on the cadet is very small and full power loads might bulge the chamber.  I was assured the rifle had only fired factory ammo...convinced I was not.

 

I have a BSA Cadet I built in 35/30-30; I have to turn the rims a little so it will feed.  The 30-30 case is 2.039 and the Maximum is 1.605.  The Cadet action I plan to use on this rifle (unless I go with the low wall) is a Greener but it should be the same action.  I considered grinding the block on the BSA but was afraid it woukld weaken the action, and turning the rims fixed the problem.  I have shot 250 gr bullets in that rifle, but those loads seemed to lossened the action so I mostly shoot 158 gr lead bullets now and 180 gr jacketed bullet for deer.
Is there a way to post pictures on this forum?
Don

I loaded up some 125 gr lead bullets behind 12 grs of Unique the other week to plink at turtles at our hunting club pond the other week; they were a fun load.  It just occured to me that I am shooting all the bullet weight now in the 35/30-30 that I was thinking about in the 35 Maximum.  I guess what appealed to me was the concept of being able top shoot the 4 case sizes in the Maximum rifle.
I am also thinking about a 20 cal wildcat based on the maxium case.  I also have a Martini in what I call the 20 Raven, which is a rimmed, blown out 20 Var Tarq that is based on the 360 DW (1.40".  I'm getting a little over 3800 fps with a 32 gr bullet.  It is capable of more speed but the cases won't eject if I push it.  The Maximum (1.605")based 20 cal would be a "Super Raven".   
I am a Martini nut and have Cadets in 17 AB, 218 Bee, 20 Raven and 35/30-30.  The only downside I have found is the weak ejection.

Somebody advise how to post pics and I will post pics of my Martini's.

Don

what do you want for your action?  What is the advantage in going with the 12/15 over the Cadet action.  I bush my firing pins, but as you know, the Cadet is already CF , so no more work is needed on the block.
You mentioned your action is a large action, which model and caliber?

Don

i don't know what action. it is a big mother that has been engraved and blessed by local witch doctor $300. 12/15s are thicker easy to stock and convert to cf

Wouldn't the .357max. be a little much for a Low Wall?

Something to keep in mind here is that (if memory serves me correctly) the .357 Rem Maximum operates at about 50,000 CUP in its factory form. This is what caused the problems which lead to the discontinuance of revolvers chambered for it (excepting the Dan Wessons). Not an issue for lead bullet shooting but for max loads it is a hot number and could make a difference which action one would use for it.